Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180929
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
329 AM CST Wed Jan 18 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 329 PM CST Tue Jan 17 2017

Very expansive shield of low clouds hanging on tight this afternoon
across the area, with the back edge of the clouds out around Omaha
and Topeka. Forecast soundings are not in too much of a hurry to get
rid of this, with a tight inversion through sunrise, although
lowering down to around 2000 feet by sunrise. NAM and GFS don`t
really show anything breaking through until closer to midday
Wednesday north of I-74, but do show the clouds starting to break
out toward mid-morning across the southwest CWA. Have kept skies
mostly cloudy through the morning, but most of the area should be
seeing some sunshine by afternoon as a ridge of high pressure drifts
eastward.

With the clouds sticking around tonight, have leaned more toward the
NAM MOS guidance, with lows mainly lower 30s, except mid 30s south
of I-70. Wednesday temperatures will be dependent on how fast the
low clouds break, but mid-upper 40s appear feasible, especially over
the southwest CWA.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 329 PM CST Tue Jan 17 2017

High pressure moving off to the east will allow moisture to return
to the area just ahead of the next weather system coming out of the
southern plains. This moisture will interact with a
developing/deepening system to bring precipitation to the CWA
beginning Thursday and continuing into Thur night. Models have
shifted the track of this system little further northwest of
previous forecast, moving it across southern and southeast IL. With
the further northwest track and the warmer temps, all precip should
be in the form of rain through the period. Based on this track, also
seeing an increase in MUCAPE in southern IL, so have included schc
of thunder in southeast and eastern IL Thur afternoon through
Thursday night. As the surface trough and 500mb trough move through,
precip chances will continue Friday morning, but then should become
dry for the afternoon as things push off to the east and northeast.

Upper level flow will then become more southwest with an upper level
low pressure area to the west and northwest. This setup will
continue to bring warm air into the region and an isolated threat of
diurnal type precip...for into the weekend. For now, will just keep
small chances in the grids to account for this. The next main threat
of precip will begin Sunday and then increase through Sunday night
and Monday. Models show significant differences as to timing,
location, and intensity of the system so pops are in for more
periods than probably will occur. However, best chances look to be
Sun night and Mon.

Temps will warm rest of the week and into the weekend, with mildest
temps being Saturday when some spots could reach the lower 60s.
After the system on Sunday, temps will cool down a bit, but still
remain above normal for this time of year.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1131 PM CST Tue Jan 17 2017

Main challenge for this TAF update is the timing of when the
IFR/LIFR ceilings will depart central and eastern Illinois
Wednesday. In the meantime, am expecting the clouds to persist
through the remainder of the night, with the lowest ceilings
ranging from 300-700 ft. Visibility is expected to be lowest in
the slightly cooler air along the I-74 corridor, with 2-3SM common
toward daybreak.

Many of the short range models seem to be overly optimistic about
pushing the low level moisture and associated cloudiness out of
the area shortly after daybreak Wednesday. The typical rule of
thumb this time of the year is for the low clouds to depart slower
than indicated by the models. As a result, will hold off on
scattering out the cloud cover about 3 hours or so slower than the
models. KSPI should be the first to clear just before 17z or so,
with KCMI scattering out around 19-20z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Miller



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